Influence Discussion Of Parameter Errors On Calculation Flow Using Flow Influence Line Method

Abstract:The design flow is an important parameter for bridge design and maintenance. The accuracy of calculation result is of great significance to the safety of bridge. The flow influence line method is one method to calculate the design flow, which based on two basic theories:the influence line method in structural mechanics and the instantaneous unit line method. It is mainly used in medium and small watershed hydrological calculation. And it is applied and promoted for its convenience, because the method needs no measurement of river channel length and watershed area of field.The direct parameters of flow influence line method are rising duration t1,falling duration t2,rainfall load R(n) and influence line peak value Cumax`t1is related to the river channel length L and flow velocity of calculating range V.And t2is determined in accordance with the proportion and t1. Rainfall load consists of calculation rainfall load Rb and calibration rainfall load Rb, and error origin includes numerical accuracy error and discretization error. Cumax is the ratio of the corresponding flow Qb by historical flood water mark and the most unfavorable flowQb under calibration rainfall load. The direct parameters of Qb are t1, t2and Rb,while Qb is determined by river channel roughness n,river channel slope I,wetted perimeter x and wetted cross-section area ω.At present, there is no systematic analysis about parameters error analysis of flow influence line method. Therefore it cannot master what the key parameters are on the whole, so how to improve the accuracy by effective measurement is impossible. This paper analyzes each parameter fluctuation’s error analysis in detail through the calculation process of flow influence line method. Then according to the error propagation theory, the comprehensive error analysis of the method is obtained. And effective improvement suggestions are put forward based on the conclusions. This paper uses the Visual Basic programming software to analyze the error of each parameter fluctuations on the final result according to the calculation process, and then makes a comprehensive error analysis according to the theory of error propagation.In this paper, through the programming calculation, it obtains the influence extent of each parameter fluctuation on the calculation result, and on the basis of accuracy of hydrological measurement parameters. The conclusion can be used for reference in the bridge hydrological survey, and it is conducive to further improve the calculation precision of flow influence line method, further popularizes the design flow calculation method.